This invention relates to flexible materials which reflect, i.e. hardly pass electromagnetic waves having frequencies used in the electric communication or the like.
Since miniaturization of electronic instruments has been advanced lately, there is a tendency of casings of these materials turning from metals to plastics. On account of this tendency, mutual interference of electronic instruments and interference of communication are increasing remarkably and strengthening of the shielding of electronic instruments from electromagnetic waves is becoming necessary. Known materials having large capacity for shielding from electromagnetic waves are mostly hard and strong materials, lacking in flexibility. It is essentially difficult to shape into a flexible structure having a large capacity for shielding from electromagnetic waves.
It is an object of the present invention to provide flexible electromagnetic-wave-shielding materials comprising carbon fibers, which materials are difficult to be produced from metals.
As a shielding method from electromagnetic waves of a frequencies used in the electric communication or radar, there is a method of absorbing electromagnetic waves or a method of reflecting it. Of these two, for the method of absorbing electromagnetic wave, satisfactory materials has not been found because materials having an absorption factor which shows small dependency on frequency are few.
For reflecting electromagnetic waves, it has been known from old time that use of a material of high electric conductivity serve the purpose. For preventing the interference of the electric communication, an electronic instrument casing made of a metal a shieldcovering of an electric wire by braiding of a metal wire, etc. have been hitherto used.
The problem of conventional electromagnetic wave shielding apparatus has been in the point of difficulty of shaping of small sized one and also in the point of extremely high cost compared with shaping of plastics in case of casings or the like. In case of shield covering wire, the problem has been that the wire is hard and thick and wiring in narrow spaces is difficult.
For the above-mentioned reason, electronic instruments which neglect the shielding from electromagnetic waves has increased. Thus the interference between instruments and the interference of communication have increased and further, the occurrence of accident on account of malfunction has been frequent. From the reconsideration of such status, the shielding of electronic instruments from electromagnetic waves has been recently promoted. Further, for the purpose of prevention of accidents, regulation by law has now been advanced.
For the shielding of casings made of plastics from electromagnetic waves, a process of flame coating of zinc, a process of coating with an electroconductive coating material or a process for preparing electroconductive plastics casing has now being used. These processes are effective for casings having definite shape, but it is the present status that a satisfactory material has not been obtained to which particular flexibility and elasticity are required, e.g., an electric wire, etc.
For the flexible shielding materials from electromagnetic waves, a metal foil, a vacuum evaporation metal film, a metal electroplated film have been used, but the metal foil has a drawbacks in that strength is low and shape stability is poor. In case of vacuum evaporation metal film and the metal electroplated film there are problems in that cost is high and reflection capability of electromagnetic waves is not sufficient.
As the flexible shielding materials from electromagnetic waves, metal nets are also useful, but when a contact resistance of the metal wire is large, since electromagnetic waves leak from the mesh of the metal nets, shielding capacity is small and moreover there is a general problem in its poor durability.
The shielding from electromagnetic waves used for radar, has two objects, i.e. the one is to cancel the disturbance of electronic instruments, etc. and the other is to camouflage the radar. In radar camouflage, there is a type which is spread in air and another type which covers facilities on the ground. For the former, small flakes of metal foils are used. As this usage does not require the durability there is no special problem. For the latter, it is very difficult to use, because the durability is required and moreover the visual camouflage is required also.
For such use, it is necessary to deal with a combination of several kinds of material which have a good coating property and a good adhesive property.
An object of the present invention is, as abovementioned, to overcome the problems of the conventional shielding material for electromagnetic waves, i.e. lack of flexibility.
The above-mentioned object can be overcome by the flexible material for reflecting electromagnetic waves of the present invention.